1. Field of the Invention
The present invention relates to a shallow trench isolation process or the like for use in the manufacturing of semiconductor devices. More particularly, the present invention relates to a method of filling trenches in a substrate during the manufacturing of a semiconductor device.
2. Description of the Related Art
Shallow trench isolation (hereinafter, referred to as ‘STI’) is a technique used in the manufacturing of semiconductor devices. Specifically, STI is used to electrically isolate conductive patterns on a surface of a substrate. In general, an STI process includes forming a trench of a given depth in the substrate, filling the trench with an insulation layer, and planarizing the insulation layer to expose the substrate. As semiconductor devices become more highly integrated, i.e., as conductive patterns become smaller and/or more densely packed on the surface of a substrate, the STI process is becoming increasingly important in the overall scheme of the semiconductor manufacturing process. In this respect, trenches in the substrate must be made narrower and deeper to increase the degree to which a semiconductor device can be integrated, e.g., to provide room for the conductive patterns of a highly integrated semiconductor device.
In addition, the STI process must be reproducible. In this respect, the STI process must be able to fill trenches with a high degree of consistency. However, the reproducibility of the trench-filling process decreases as the trenches become narrower and as the depth of trenches increases to meet the demand for more highly integrated semiconductor devices. In particular, voids can sometimes be left in an insulation layer formed to fill a relatively narrow and deep trench during an STI process. In this case, the voids adversely affect the reliability of the semiconductor device.
A technique of filling a trench using a high-density plasma oxide has been developed due to the rapidity at which a trench can be filled. In general, a plasma reaction is induced in process gas, a substrate provided with trenches is exposed to the plasma and, as a result, an oxide layer is formed on the substrate including within the trenches. According to this plasma enhanced chemical vapor deposition technique, the process gas is under a low pressure and is excited using a high radio frequency power. Thus, the resulting oxide layer has a high density compared to a thermal oxide layer, a USG oxide, or a BPSG oxide formed by a typical CVD process.
Moreover, in this technique, plasma ions continuously collide with the surface of the oxide layer being formed at the bottom of the trench, thereby sputtering the oxide material. Characteristically, the high-density plasma oxide layer is re-deposited on vertical surfaces that define the sides of the trench (surfaces normal to what is considered to be the direction of the plasma reaction) such that the trench is filled rapidly. Thus, the deposition layer formed by this technique has a dominant vertical characteristic.
However, material sputtered from a layer formed on the bottom of a trench and re-deposited on the side of the trench can form an overhang that blocks the top of the trench before the oxide layer completely fills the trench. In such a case, a void is formed inside that part of the high-density plasma oxide layer which occupies the trench. To avoid this problem, the overhang of the high-density plasma oxide layer is removed by isotropically etching the layer, and another high-density plasma oxide layer is formed to complete the filling of the trench. Thus, a stacked high-density plasma oxide layer is formed.
More specifically, for example, a first high-density plasma oxide layer having a given thickness is formed within a trench. Then the first high-density plasma oxide layer is wet etched to remove any overhang. Subsequently, a thermal oxide layer and a second high-density plasma oxide layer are formed, i.e., are stacked on the remaining portion of the first high-density plasma oxide, thereby filling the trench.
However, in such a method of filling a trench, the substrate must be transported to different pieces of equipment in sequentially carrying out the deposition process of forming the first high-density plasma oxide layer, the wet etching process, the deposition process of forming the thermal oxide layer, and the deposition process of forming the second high-density plasma oxide layer. Transferring the substrates between, into and out of these pieces of equipment takes time and thus detracts from the productivity of the semiconductor device manufacturing process.